The present invention relates to polysaccharide compositions, particularly to compositions of a combination of a cross-linked polysaccharide and a polysaccharide having no cross-linking.
Aqueous soluble polysaccharides such as the natural gums, e.g., guar gum, and the aqueous soluble derivatives of a polysaccharide such as the cellulose ethers are employed in a variety of commercial applications. In general, the aqueous soluble polysaccharides or polysaccharide derivatives are dissolved in water prior to or coincident with their use. Unfortunately, many polysaccharides, and/or derivatives thereof, e.g., cellulose ethers such as hydroxypropyl methylcellulose are not readily dispersible in aqueous liquids due to the fact that the polysaccharides or derivatives are not easily wetted by cold water, thereby tending to agglomerate and form into soft lumps, balls or nodules. Thereafter, these agglomerations are extremely difficult to disperse and/or dissolve in cold water.
Heretofore, to facilitate their dispersion and subsequent dissolution, the polysaccharide or polysaccharide derivatives thereof is initially dispersed with agitation in hot water. On subsequent cooling or the addition of cold water to the resulting uniform dispersion, a solution of the polysaccharide or derivative is obtained. Unfortunately, an undesirably long time period is often required prior to complete dissolution. Moreover, since many of the other ingredients such as dyes and pigments are adversely affected by hot water, the direct formulation of aqueous compositions containing the dissolved polysaccharide or derivative is often not possible. Therefore, it is frequently necessary to prepare a separate solution of the cellulose ether and to subsequently mix the resulting solution with a solution or suspension of other ingredients to obtain the desired, final composition.
Various other means have also been proposed to reduce the difficulty of and time for dissolving cellulose ethers and other polysaccharides or polysaccharide derivatives in aqueous liquids. For example, thoroughly blending particles of an aqueous soluble cellulose ether with another dry powder such as calcium carbonate prior to the ether's addition to water assists in achieving a uniform dispersion of the cellulose ether. Unfortunately, the blended dry powder ingredients often affect the properties of the resulting composition and are not always compatible with the composition's other ingredients.
Alternatively, U.S. Pat. No. 2,647,064 discloses that particles of a cellulose ether having a surface active agent incorporated therein are more readily dissolvable in cold water. (See also, U.S. Pat. No. 2,720,464.) Unfortunately, large amounts of the surface active agent are required to prepare a readily dissolvable cellulose ether, thereby rendering the treated particles unsuitable for use in many applications.
In another method for improving the cold water dispersibility of a cellulose ether or other polysaccharide derivative, U.S. Pat. No. 2,879,268 discloses treating the cellulose ether with small amounts of a cross-linking agent such as formaldehyde or a dialdehyde such as glyoxal. The resulting, lightly cross-linked cellulose ethers can be added directly to cold water and subsequently dissolved without the formation of soft lumps or other agglomerations. In general, the addition of an ammonium or alkali metal salt of a weak protonic acid with the lightly cross-linked cellulose ethers will further improve the cold water solubility thereof by reducing the time for complete dissolution to occur. (See, for example, U.S. Pat. No. 3,357,519.) Unfortunately, in many cases, particularly in soft and/or cold water, the cross-linked cellulose ether dissolves at a sufficiently slow rate that, without continuous agitation, the cellulose ether settles to the bottom of the aqueous liquid. This settling results in slow increase in the viscosity of the aqueous liquid and yields a nonuniform solution which contains undissolved, agglomerated particles of the cellulose ether.
In view of the stated deficiencies in the prior art, it remains highly desirable to provide a composition of a polysaccharide or polysaccharide derivative which polysaccharide or derivative is readily dissolved in cold water without the formation of agglomerations, soft lumps or nodules in the absence of continuous agitation.